Codeforce Problem 821: Double Cola

DoubleCola.hs

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections #-}
{-
Double Cola
https://codeforces.com/problemset/problem/82/A

EFFICIENCY REQUIREMENTS

time limit per test: 1 second
memory limit per test: 256 megabytes
input: standard input
output: standard output

PROBLEM

Sheldon, Leonard, Penny, Rajesh and Howard are in the queue for a "Double Cola"
drink vending machine; there are no other people in the queue. The first one in
the queue (Sheldon) buys a can, drinks it and doubles! The resulting two
Sheldons go to the end of the queue. Then the next in the queue (Leonard) buys
a can, drinks it and gets to the end of the queue as two Leonards, and so on.
This process continues ad infinitum.

For example, Penny drinks the third can of cola and the queue will look like
this: Rajesh, Howard, Sheldon, Sheldon, Leonard, Leonard, Penny, Penny.

Write a program that will print the name of a man who will drink the n-th can.

Note that in the very beginning the queue looks like that: Sheldon, Leonard,
Penny, Rajesh, Howard. The first person is Sheldon.

INPUT

The input data consist of a single integer n (1 ≤ n ≤ 109).

It is guaranteed that the pretests check the spelling of all the five names,
that is, that they contain all the five possible answers.

OUTPUT

Print the single line — the name of the person who drinks the n-th can of cola.
The cans are numbered starting from 1. Please note that you should spell the
names like this: "Sheldon", "Leonard", "Penny", "Rajesh", "Howard" (without the
quotes). In that order precisely the friends are in the queue initially.

EXAMPLES

1 -> Sheldon
6 -> Sheldon
1802 -> Penny

-}
data BigBangCharacter
  = Sheldon
  | Leonard
  | Penny
  | Rajesh
  | Howard
  deriving (Enum, Eq, Show)


queue :: [(BigBangCharacter, Int)]
queue = map (,1) [Sheldon .. Howard]


doubleCola :: Int -> [(BigBangCharacter, Int)] -> BigBangCharacter
doubleCola n characters = do
  let
    ([(firstChar, clones)] :: [(BigBangCharacter, Int)], rest) = splitAt 1 characters
  if n == 0 || clones >= n
    then firstChar
    else doubleCola (n - clones) (rest ++ [(firstChar, clones * 2)])


tests :: IO ()
tests = do
  test Sheldon 1
  test Sheldon 6
  test Penny 52
  test Penny 1802
  test Leonard 7230702951
 where
  test :: BigBangCharacter -> Int -> IO ()
  test c n = print $ c == doubleCola n queue